Switching mode power supply and driving method

• US 7,672,146 B2
• Filed: 05/29/2007
• Issued: 03/02/2010
• Est. Priority Date: 10/13/2006
• Status: Expired

• Current Assignee: Fairchild Semiconductor Corporation (ON Semiconductor Corporation)
• Original Assignee: Fairchild Korea Semiconductor Limited (ON Semiconductor Corporation)
• Inventors: Park, Young-Bae, Koo, Gwan-Bon
• Primary Examiner(s): BERHANE, ADOLF D
• Application Number:
  US11/807,460
• Publication Number:
  US 20080089100A1
• Time in Patent Office: 1,008 Days
• Field of Search: 363/20, 363/21.01, 363/21.04, 363/21.08, 363/21.1, 363/21.11, 363/21.12, 363/21.16, 363/21.18, 363/95, 363/97
• US Class Current: 363/21.01
• CPC Class Codes: H02M 3/33515 with digital control
• CPC Class Codes: H02M 3/33523 with galvanic isolation between input and output of both the power stage and the feedback loop

Abstract

A switching mode power supply includes a switching transistor, coupled to a primary coil at a primary side of a transformer for converting an input DC voltage, supplying power to a secondary and a tertiary coil at a secondary side of the transformer according to an operation of the switching transistor; a switching controller receiving a feedback voltage corresponding to a first voltage generated in the secondary coil and receiving a detection signal corresponding to a current of the switching transistor to generate a switching control signal for controlling the turn on/off of the switching transistor; and a feedback signal generator receiving the first voltage and the switching control signal to set a sampling period, and storing the first voltage, sampled with a last pulse of the first pulse string within the sampling period as a feedback voltage. The output voltage is thereby accurately detected without opto-couplers or shunt regulators.

Claims

1. A switching mode power supply comprising:

a power supply unit comprising a switching transistor, coupled to a primary coil at a primary side of a transformer for converting an input DC voltage and that supplies power to a secondary coil and a tertiary coil at a secondary side of the transformer according to an operation of the switching transistor;

a switching controller configured to receive a feedback voltage corresponding to a first voltage generated in the tertiary coil at the secondary side of the transformer, and to receive a detection signal corresponding to a current flowing to the switching transistor to generate a switching control signal for controlling the turn on/off of the switching transistor; and

a feedback signal generator configured to receive the first voltage and the switching control signal to set a sampling period, and to set a voltage level of the first voltage that is sampled by one pulse of a first pulse string within the sampling period as a feedback voltage, using a plurality of pulse strings comprising the first pulse string and a second pulse string, having a plurality of pulses.

2. The switching mode power supply of claim 1, configured to toggle the plurality of pulse strings with different timing.

3. The switching mode power supply of claim 1, configured so that the second pulse string comprises a first pulse that is a most adjacent pulse to an ending time of the sampling period among a plurality of pulses of the plurality of pulse strings, and the one pulse is a pulse that precedes the first pulse.

4. The switching mode power supply of claim 3, wherein the one pulse is a pulse that immediately precedes the first pulse.

5. The switching mode power supply of claim 4, wherein the feedback signal generator comprises:

a first signal generator configured to receive the switching control signal to generate a first signal;

a first logical operation unit configured to receive the first voltage and a reference voltage to a first terminal and a second terminal respectively, and makes comparison between the first voltage and the reference voltage to generate a second signal;

a second logical operation unit configured to receive the second signal and the first signal to a third terminal and a fourth terminal respectively, and configured to invert an output signal in an immediately preceding state at a first time in which the second signal is in a first level and the first signal changes to a second level and at a second time in which the first signal is in a third level and the second signal first changes to a fourth level after the first time;

a pulse string generator configured to generate the plurality of pulse strings;

a sampling unit configured to store a voltage level of the first voltage corresponding to pulses of the plurality of pulse strings during a period from the first time to the second time; and

a sampling signal output controller configured to output a voltage level of the first voltage that is sampled with the one pulse.

6. The switching mode power supply of claim 5, wherein the first signal generator is configured to generate the first signal a seventh level during a first period corresponding to a time at which the switching control signal changes from a fifth level to a sixth level, and to generate the first signal eighth level during a second period that is a period off the first period, and

the second logical operation unit is configured to set the sampling period by performing a logical operation between the first signal and the second signal.

7. The switching mode power supply of claim 6, wherein the sampling period is configured to start substantially when the first signal changes from the eighth level to the seventh level.

8. The switching mode power supply of claim 6, wherein the first logical operation unit is configured to generate the second signal ninth level when the first voltage is higher than the reference voltage, and is configured to generate the second signal tenth level when the first voltage is lower than the reference voltage.

9. The switching mode power supply of claim 8, wherein the sampling period ends at a time that the second signal changes from the ninth level to the tenth level.

10. The switching mode power supply of claim 8, wherein the first signal changes to the seventh level after the second signal changes from the tenth level to the ninth level, and returns to the eighth level before a time of ending of the sampling period.

11. The switching mode power supply of claim 8, wherein the reference voltage is a ground voltage.

12. The switching mode power supply of claim 8, wherein the first signal changes from the eighth level to the seventh level at the first time and the second signal changes from the ninth level to the tenth level at the second time, as a voltage that is applied to the switching transistor starts resonance.

13. The switching mode power supply of claim 11, wherein the sampling unit comprises:

third logical operation units configured to receive an output signal of the second logical operation unit and one of the plurality of pulse strings to perform an AND operation; and

latches that receive an output signal of the third logical operation units as a driving timing signal and that sample a voltage level of the first voltage when the driving timing signal changes to an eleventh level,

wherein the number of third logical operation units and latches corresponds to that of the plurality of pulse strings.

14. The switching mode power supply of claim 13, wherein the feedback signal generator comprises:

a selection switch that is driven by control of the sampling signal output controller and that is selectively connected to an output terminal of a latch among the latches with one end; and

a sampling signal output unit that is connected to the other end of the selection switch to transfer a voltage level that is sampled with the one pulse, which is input through the selection switch to the switching controller.

15. The switching mode power supply of claim 14, wherein the sampling signal output unit is configured to transfers the voltage level to the switching controller until it receives a different voltage level through the selection switch.

16. The switching mode power supply of claim 15, wherein the sampling signal output unit selectively outputs a voltage level that is transferred through the switch according to a driving timing signal that is input from the sampling signal output controller.

17. The switching mode power supply of claim 16, wherein the sampling signal output controller applies a control signal to the switch at the second time and transfers a driving timing signal of a twelfth level to the sampling signal output unit.

18. The switching mode power supply of claim 17, wherein the first level, the third level, the fifth level, the eighth level, the ninth level, the eleventh level, and the twelfth level are corresponding logical high levels, and the second level, the fourth level, the sixth level, the seventh level, and the tenth level are corresponding logical low levels.

19. The switching mode power supply of claim 17, wherein the pulse generator comprises a pulse string generator for generating the plurality of pulse strings, and the sampling signal output controller comprises pulse string input terminals of a the number that corresponds to that of the pulse string generators to receive the plurality of pulse strings through a different pulse input terminal.

20. The switching mode power supply of claim 19, wherein the sampling signal output controller stores the number of pulse string generators and information on the latch corresponding to the pulse string generators, and

in the sampling period, the sampling signal output controller stores a pulse input order of the pulse string input terminal for receiving the pulse strings until a number of pulses corresponding to that of the pulse string generators is input from a first input pulse among the plurality of pulse strings that are input through the pulse string input terminal, and connects the switch to an output terminal of a latch corresponding to the one pulse at the second time.

21. The switching mode power supply of claim 20, wherein the feedback signal generator further comprises a filter configured to convert a sudden change of the voltage level that is output from the sampling signal output unit into a substantially linearly changing voltage and transferring the linearly changing voltage to the switching controller.

22. The switching mode power supply of claim 21, wherein the filter is a low pass filter.

23. The switching mode power supply of claim 1, wherein the switching controller is configured to compare the feedback voltage with the detection signal, and to control the switching transistor to turn on/off according to the comparison result to decrease energy that is induced to a secondary side of the transformer if the feedback voltage is higher than a voltage level of the detection signal and increase energy that is induced to a secondary side of the transformer if the feedback voltage is lower than a voltage level of the detection signal.

24. The switching mode power supply of claim 1, wherein the switching transistor, the switching controller, and the feedback signal generator are formed in a single chip.

25. The switching mode power supply of claim 1, wherein the switching controller and the feedback signal generator are formed in a single chip and the switching transistor is formed in a separate chip.

26. A switching mode power supply for generating an output DC voltage by converting a DC voltage, the switching mode power supply comprising:

a PWM controller comprising a switching transistor with a first stage connected to an input terminal of a DC voltage and that controls the switching transistor to drive according to a voltage level of a first voltage corresponding to the output DC voltage;

an output unit comprising an inductor with one end connected to a second stage of the switching transistor, a capacitor with one end connected to the other end of the inductor, and a diode with an anode connected to the other end of the capacitor and with a cathode connected to one end of the inductor, the output unit being configured to generate the output DC voltage according to turning on/off of the switching transistor; and

a voltage distribution unit configured to distribute a voltage across the inductor to generate the first voltage,

wherein the PWM controller further comprises

a switching controller configured to receive a feedback voltage corresponding to the first voltage to generate a switching control signal for controlling the switching transistor to turn on/off, and

a feedback signal generator configured to receive the switching control signal and the first voltage to set a sampling period and that sets a voltage level of the first voltage that is sampled by one pulse of a first pulse string within the sampling period as a feedback voltage using a plurality of pulse strings comprising the first pulse string and a second pulse string having a plurality of pulses.

27. The switching mode power supply of claim 26, wherein switching mode power supply is configured to toggle the plurality of pulse strings with different timing.

28. The switching mode power supply of claim 26, wherein the second pulse string comprises a first pulse that is a most adjacent pulse to an ending time of the sampling period among a plurality of pulses of the plurality of pulse strings, and the one pulse is a pulse that is preceded the first pulse.

29. The switching mode power supply of claim 28, wherein the one pulse is a pulse that immediately precedes the first pulse.

30. The switching mode power supply of claim 29, wherein the feedback signal generator comprises:

a first signal generator that receives the switching control signal to generate a first signal;

a first logical operation unit that receives the first voltage and a reference voltage to a first terminal and a second terminal respectively, and makes comparison between the first voltage and the reference voltage to generate a second signal;

a second logical operation unit that receives the second signal and the first signal to a third terminal and a fourth terminal respectively, and configured to invert an output signal in an immediately preceding state at a first time in which the second signal is in a first level and the first signal changes to an second level and at a second time in which the first signal is in a third level and the second signal first changes to a fourth level after the first time;

a pulse string generator that generates the plurality of pulse strings;

a sampling unit that stores a voltage level of the first voltage corresponding to pulses of the plurality of pulse strings during a period from the first time to the second time; and

a sampling signal output controller that outputs a voltage level of the first voltage that is sampled with the one pulse.

31. The switching mode power supply of claim 30, wherein the first signal generator generates the first signal a seventh level during a first period corresponding to a time at which the switching control signal changes from a fifth level to a sixth level, and generates the first signal eighth level during a second period that is a period off the first period, and

the second logical operation unit sets the sampling period by performing a logical operation between the first signal and the second signal.

32. The switching mode power supply of claim 31, wherein the sampling period starts substantially when the first signal changes from the eighth level to the seventh level.

33. The switching mode power supply of claim 31, wherein the first logical operation unit generates the second signal ninth level when the first voltage is higher than the reference voltage, and generates the second signal tenth level when the first voltage is lower than the reference voltage.

34. The switching mode power supply of claim 33, wherein the sampling period ends at a time that the second signal changes from the ninth level to the tenth level.

35. The switching mode power supply of claim 33, wherein the first signal changes to the seventh level after the second signal changes from the tenth level to the ninth level, and returns to the eighth level before a time of ending of the sampling period.

36. The switching mode power supply of claim 33, wherein the reference voltage is a ground voltage.

37. The switching mode power supply of claim 33, wherein the first signal changes from the eighth level to the seventh level at the first time and the second signal changes from the ninth level to the tenth level at the second time, as a voltage that is applied to the switching transistor starts resonance.

38. The switching mode power supply of claim 37, wherein the sampling unit comprises:

third logical operation units configured to receive an output signal of the second logical operation unit and one of the plurality of pulse strings to perform an AND operation; and

latches that receive an output signal of the third logical operation units as a driving timing signal and that sample a voltage level of the first voltage when the driving timing signal changes to an eleventh level,

wherein the number of third logical operation units and latches corresponds to that of the plurality of pulse strings.

39. The switching mode power supply of claim 38, wherein the feedback signal generator comprises:

a selection switch that is driven by control of the sampling signal output controller and that is selectively connected to an output terminal of a latch among the latches with one end; and

a sampling signal output unit that is connected to the other end of the selection switch to transfer a voltage level that is sampled with the one pulse, which is input through the selection switch to the switching controller.

40. The switching mode power supply of claim 39, wherein the sampling signal output unit is configured to transfers the voltage level to the switching controller until it receives a different voltage level through the selection switch.

41. The switching mode power supply of claim 40, wherein the sampling signal output unit selectively outputs a voltage level that is transferred through the switch according to a driving timing signal that is input from the sampling signal output controller.

42. The switching mode power supply of claim 41, wherein the sampling signal output controller applies a control signal to the switch at the second time and transfers a driving timing signal of a twelfth level to the sampling signal output unit.

43. The switching mode power supply of claim 42, wherein the first level, the third level, the fifth level, the eighth level, the ninth level, the eleventh level, and the twelfth level are corresponding logical high levels, and the second level, the fourth level, the sixth level, the seventh level, and the tenth level are corresponding logical low levels.

44. The switching mode power supply of claim 42, wherein the pulse generator comprises a pulse string generator for generating the plurality of pulse strings, and the sampling signal output controller comprises pulse string input terminals of a the number that corresponds to that of the pulse string generators to receive the plurality of pulse strings through a different pulse input terminal.

45. The switching mode power supply of claim 44, wherein the sampling signal output controller stores the number of pulse string generators and information on the latch corresponding to the pulse string generators, and

in the sampling period, the sampling signal output controller stores a pulse input order of the pulse string input terminal for receiving the pulse strings until a number of pulses corresponding to that of the pulse string generators is input from a first input pulse among the plurality of pulse strings that are input through the pulse string input terminal, and connects the switch to an output terminal of a latch corresponding to the one pulse at the second time.

46. The switching mode power supply of claim 45, wherein the feedback signal generator further comprises a filter configured to convert a sudden change of the voltage level that is output from the sampling signal output unit into a substantially linearly changing voltage and transferring the linearly changing voltage to the switching controller.

47. The switching mode power supply of claim 46, wherein the filter is a low pass filter.

48. The switching mode power supply of claim 26, wherein the switching controller controls the switching transistor to turn on/off according to a voltage level of the feedback voltage to change the output DC voltage.

49. The switching mode power supply of claim 26, wherein the first stage and the second stage of the switching transistor are a drain and a source, respectively.

50. A driving method of a switching mode power supply that supplies power to a secondary coil at a secondary side of the transformer according to an operation of a switching transistor that is coupled to a primary coil at a primary side of a transformer and that generates an output DC voltage by converting an input DC voltage of a primary side of transformer,

wherein the secondary side of the transformer comprises the secondary coil, a first diode with an anode connected to one end of the secondary coil, and a first capacitor with a first stage connected to a cathode of the first diode and with a second stage connected to a ground stage and the other end of the secondary coil,

wherein the driving method comprises:

(a) setting a sampling period;

(b) sampling a voltage level of the first voltage that is generated at the secondary side of the transformer using a plurality of pulse strings comprising a first pulse string having a plurality of pulses; and

(c) generating a switching control signal that controls the switching transistor to turn on/off using a voltage level that is sampled by one pulse of the first pulse strings within the sampling period as a feedback voltage among voltage levels that are sampled at step (b).

51. The driving method of claim 50, wherein the one pulse is a previous pulse of a pulse most adjacent to an ending time of the sampling period within the sampling period.

52. The driving method of claim 51, wherein the one pulse is a pulse that immediately precedes the pulse most adjacent to an ending time of the sampling period.

53. The driving method of claim 50, wherein the plurality of pulse strings are toggled with different timing.

54. The driving method of claim 50, wherein

step (a) comprises the sampling period is set by a logical operation between a first signal that is sustained a third level during a first period corresponding to a time at which the switching control signal changes from a first level to a second level and sustained a fourth level and sustained a fourth level off the first period, and a second signal set by a result of a comparison between the first voltage and a reference voltage.

55. The driving method of claim 54, wherein the second signal is in a fifth level if the first voltage is higher than the reference voltage and if the first voltage is lower than the reference voltage, the second signal is in a sixth level, and the first signal returns to the fourth level before ending of the sampling period after it changes to the third level, after the second signal changes from the sixth level to the fifth level.

56. The driving method of claim 55, wherein the sampling period starts at a time at which the first signal changes from the fourth level to the third level and ends at a time at which the first signal changes from the fifth level to the sixth level as a voltage that is applied to the switching transistor starts resonance.

57. The driving method of claim 56, wherein the first level, the fourth level, and the fifth level are a high level, and the second level, the third level, and the sixth level are a low level.

58. A driving method of a switching mode power supply for generating an output DC voltage by converting a DC voltage,

wherein the switching mode power supply is a non-isolated switching mode power supply that changes the output DC voltage that is output through an output unit according to an operation of a PWM controller that comprises a switching transistor with a first stage connected to an input terminal of the DC voltage, and

the output unit comprises an inductor with one end connected to a second stage of the switching transistor, a capacitor with one end connected to the other end of the inductor, and a first diode with an anode connected to the other end of the capacitor and with a cathode connected to one end of the inductor,

wherein the driving method comprises:

(a) setting a sampling period;

(b) sampling a voltage level of the first voltage that is generated by distributing a voltage that is applied to both ends of the inductor using a plurality of pulse strings comprising a first pulse string having a plurality of pulses; and

(c) generating a switching control signal that controls the switching transistor to turn on/off using a voltage level that is sampled by one pulse of the first pulse string within a sampling period as a feedback voltage among voltage levels that are sampled at step (b).

59. The driving method of claim 58, wherein the one pulse is a previous pulse of a pulse most adjacent to an ending time of the sampling period within the sampling period.

60. The driving method of claim 59, wherein the one pulse is a pulse that immediately precedes the pulse most adjacent to an ending time of the sampling period.

61. The driving method of claim 58, wherein the plurality of pulse strings are toggled with different timing.

62. The driving method of claim 58, wherein

at step (a), the sampling period is set by a logical operation between a first signal that is sustained a third level during a first period corresponding to a time at which the switching control signal changes from a first level to a second level and sustained a fourth level and sustained a fourth level off the first period, and a second signal set by a result of a comparison between the first voltage and a reference voltage.

63. The driving method of claim 62, wherein the second signal is in a fifth level if the first voltage is higher than the reference voltage and if the first voltage is lower than the reference voltage, the second signal is in a sixth level, and the first signal returns to the fourth level before ending of the sampling period after it changes to the third level, after the second signal changes from the sixth level to the fifth level.

64. The driving method of claim 63, wherein the sampling period starts at a time at which the first signal changes from the fourth level to the third level and ends at a time at which the first signal changes from the fifth level to the sixth level as a voltage that is applied to the switching transistor starts resonance.

65. The driving method of claim 64, wherein the first level, the fourth level, and the fifth level are a high level, and the second level, the third level, and the sixth level are a low level.